High stability greases



United States Patent HIGH STABILITY GREASES John M. Musselman, Brecksville, and Charles H. Whitacre, South Euclid, Ohio, assignors to The Standard Oil Company, Cleveland, Ohio, a corporation of Ohio No Drawing. Application April 2, 1954 Serial No. 420,748

15 Claims. (Cl. 252-41) This invention relates to greases having high consistency stability and high oxidation stability, containing a 2,824,064 Patented Feb. 18, 71958 "ice Another important property of a grease lubricant is resistance to oxidation, and this is referred to as oxidation stability. This property is measured by the so-called tentative A. S. T. M. Norma-Hoffman method, which involves dividing a gram sample of the grease into five equal parts, placing each part in a Pyrex dish, and placing these dishes on racks in a vertical cylindrical stainless steel bomb, connected to a pressure recorder for measuring pressure drop. This bomb is very similar to the induction bomb used in gasoline testing. The. bomb is immersed in a 210 F. constant temperature oil bath during the test, and the material being tested is subjected to an initial-oxygen pressure of 110 p. s. i. g. (pounds per square inch gauge). The loss in pressure with time is measured, and a loss of ten pounds or less in 100 hours is regarded as equivalent to a satisfactory stability for at least two years; and a loss of five pounds or less is preferable.

ing an iodine value in the range of about 55 to about 77, the soap being substantially free of glycerin and glycerin reaction products and polyolefinic fatty acids.

activities of the grease maker, and a relatively limited amount of development work in the grease industry.

The grease lubricant demands of present day machinery are not satisfied by the older lubricants, i. e., in the automotive, aviation, special machinery, and the like fields.

A most important characteristic of grease lubricants is the ability to withstand mechanical shear without undue loss in consistency, and this is referred toas consistency stability. This property is measured in terms of penetration at 77 F. using an A. S. T. M. conical type penetrometer. The grease is mechanically worked in an A. S. T. M. grease worker, which essentially consists of a piston and cylinder assembly, wherein the piston is a disk having many relatively small perforations. The cylinder is charged with grease, and the piston reciprocated, thus rapidly forcing the grease through the perforations. For the present purposes, the penetration is measured, after working 0, 6.0, and 10,000 strokes.

In accordance with the invention, it has been found that when an oil having a viscosity index of not over 87 is used in making a grease, the use of soaps of fatty acids having a certain range of iodine value has particular advantages, and that there is a critical relationship between the degree of unsaturation of the fatty acid and the kind of unsaturation (whether monoolefinic or polyolefinic) of the fatty acid, and the oxidation stability of the grease and the consistency stability of the grease upon mechanical working.

The objects achieved in accordance with. the invention include the provision of soft to hard grease lubricants having very high consistency stability and oxidation stability; the provision of grease lubricants containing a mineral lubricating oil and 5 to 50% of a metal soap of a fatty acid or mixture of fatty acids having from 14 to 22 carbon atoms and an iodine value in the range of about to about 77, and substantially free of glycerin and glycerin reaction products and polyolefinic acids, i. e., not over about 5 to about 10%; fatty acids having 16 to 22 carbon atoms are preferred and the eighteen carbon atom acids are about optimum.

It will be apparent to those skilled in the art from the iodine value set forth that the fatty acids employed as a component of the metal soaps employed to thicken the lubricating oils and form greases in accordance with the invention include saturated and monoethenoid unsaturated fatty acids, which are taken in amounts to produce a final product or fatty acid mixture having an iodine value in the range from about 55 to about 77.

Among the saturated fatty acids having from 14 to 22. carbon atoms which can be used are the following:

TABLE I Saturated fatty acids Common Molecular Neutral- Systematic name name Formula weight ization value 1 n-Pentadeeanoie, pentadecoic. Pentadecylic. 014151290 OH 242. 39 231. 46 n-Hexadecanoic, hexadeeoic- Palmitie C H COOH 256. 42 218. 80 n-Heptadecanoic, heptadecoi Margario CmHsaCOOH 270. 44 207. 45 n-Octadecanoic, octadecoic Stearic. 01111350 0 OH 284. 47 197. 23 n-Nonadecanoic, nonadecoi Nonadecyl OrsHcwC O OH 298. 49 187. 96 n-Eleosanoic, eicos0ic Arachidic- CmHaiC 0 OH 312. 52 179. 52 n-Heneicosanoie, heneieosoic. CmHucOOH 326. 55 171. 31 n-Docosanoic, docosoic Behenic- OnHaOOOH 340. 57 164. 73 n-Tricosanoic, tricosolc OHH COOH 354. 60 158. 22

l The neutralization value of a monobasic fatty acid is equal to the number of milligrams of potassium hydroxide required to neutralize one gram of the acid, or 56.105X100/M. W.

acid.

hydrogenation, especially selective hydrogenation which hydrogenates the polyolefinics preferentially, and dimer izing in which the polyolefinics are polymerized and the remaining fatty acids separated from the polymer residue by distillation. If the iodine value is too low, a suflicient amount of a monoethenoid fatty acid, such as pure oleic acid, can be added.

From these fatty acids or mixtures thereof the metal soaps are prepared according to known procedures which need not be described here. The sodium soap is preferred but the alkali metal and alkaline earth metal soaps TABLE II Monoethenozd fatty acids Common Molecular Neutral- Iodine Systematic name name Formula weight lzation value value 1 A5.6-"letradecenoic 014112 0 226. 247. 87 112. 15 A9,10-'letradeeenoic Myristoleic 0 41 12601 226.35 247. 87 112. 15 A9.i0-Hexadecenoic Palmitoleic CmHanOi 254. 220. 53 99. 78 A6,? Octadecenoic- Petroselinic- 018113401 282. 198. 63 89. 87 AQJO-Octadecenolc. Oleic 013E340: 282. 45 198. 63 89. 87 CmHslOz 282. 45 198. 63 89. 87 (12011390: 310. 180. 69 81. 75 Ciel-Iss0: 310. 50 180. 69 81. 75 021114202 338. 56 165. 72 74. 98 A13,14-Docosenoic. Erucic- 092114203 338. 56 165. 72 74- 98 required to neutralize one gram of act Several of the above unsaturated acids have iodine values within the prescribed range and can be used alone, but saturated acids can be used in admixture with unsaturated acids if the mixture has the prescribed iodine values. It is evident from the iodine values quoted above that the amounts of the unsaturated and the saturated fatty acid which are required to produce a mixture having an iodine number of from to 77 are readily calculated by simple arithmetic, inasmuch as the number of grams of iodine which theoretically can be reacted with the acid depend upon the molecular weight of the acid, which is known, one molecular weight of iodine being absorbed for each molecular weight of acid.

In addition to mixtures of various saturated and unsaturated monoethenoid acids selected from the above groups, there can also be employed the mixtures of fatty aclds obtained by the splitting of naturally-occurring fats and oils, including vegetable, plant, seed, fish, animal and marine animal fats and oils, for example, sperm whale oil, butter, tallow, coconut oil, castor oil, tung oil, olive oil, rapeseed oil, mutton fat, beef fat, lard, peanut oil, cottonseed oil, linseed oil, corn oil, soybean oil, teaseed oil, cod liver oil, sardine oil, herring oil, mustard oil, and jojoba wax, provided such mixtures meet the re quirements listed heretofore. Where these mixtures have too high an iodine number or too high a polyolefinic content these can be reduced by known methods to within the desired range or by blending the fat with a saturated fatty acid. Two methods of reducing these values are tion of the grease by mixing the fatty acids with the stoichiometric amount of alkali or alkaline earth metal compound, usually the om'de or hydroxide, and with the mineral oil.

Before or after preparing the metal soaps the fatty acid or fatty acid mixture used will be freed from polyethenoid unsaturated fatty acids and glycerin and glycerin reaction products, i. e., unreacted natural fats from which the fatty acids are obtained, by hydrogenation and/or extraction or distillation techniques.

Thus, although it will be apparent that the invention is applicable both to naturally-occurring and to synthetically prepared fatty acids and mixtures thereof, the naturally-occurring materials may have to be treated by various known methods in order to bring the polyethenoid acid content and the content of glycerin and glycerin reaction products to below the maximum permitted in accordance with the invention.

The lubricating oils used in the greases of the invention are of mineral origin, and have a viscosity index below about 87. Viscosity index is a numerical value which indicates the relative resistance of a given oil to thinning out with heat or to thickening up with cold and is a function of the hydrocarbon types in the oil. The viscosity index varies with the crude from which the oil is derived, and the method and degree of refining. The

'. viscosity index also bears a direct relation to the crude source. For example, lubricating oils from Mid-Continent crude have viscosity indices of 65 to 80, and those from Pennsylvania crude around 10.0. .Many .paraffinic oils from Pennsylvania, and certain Mid-Continent crudes when highly refined by solvent extraction processes may have viscosity indices appreciably above 100. The viscosity index is an empirical and somewhat arbitrary system, inasmuch as it was established initially by assigning a viscosity index of 100 to a typical Pennsylvania oil. The viscosity index is also an index of paraffinic content, the higher the parafi'inic content the higher the viscosity index. The highly paraffinic oils with a viscosity index above 87 have too high a paraffinic content to disperse the particular soaps used in the greases of the invention.

In accordance with the instant invention, the viscosity index limit of not over about 87 excludes most of the Pennsylvania and a large number of the, Mid-Continent solvent-extracted premium lubricating oils available on the market, particularly the highly parafiini-c oils. The following table illustrates this point:

TABLE III The amount of soap may be varied as desired, according to the penetration required, but usually will lie within the range from about 5 to about 50%. Greases having from 10 to 30% soap are of medium consistency. Those having less soap are soft and those having: more soap are hard.

A large number of greases were made in which the variables extended over a. wide range. From this study the ranges enumerated heretofore were determined. In

10 order to facilitate a clear understanding of the invention,

cosity of 75 SSU at 210 F. and a viscosity index of 75.

The fatty acids used are the purest available commercially. The sodium hydroxide is a conventional 45% commercial grade. a p I,

The grease was prepared in a 50 lb. jacketed, carbon steel vessel about 13 inches in diameter and about 21--.-5

Specification tests on typical lubricating oils derived from typical crude oils 'by conventional refitting methods (not solvent-extracted Neutral Oils (Approx. SAE 10) Bright Stocks (Approx. SAE 70) Pa. Mid-Cont. Coastal Pa. Mid-Cont. Coastal Viscosity indexnut 101 76 19 100 77 Gravity (API),. F 30.2 25.8 21. 4 26.3 23.7 20.6 Saybolt viscosity at 100 F 180 205 222 2, 280 3. 370 2,100 Saybolt viscosity at 210 F 45. 3 45. 4 44. 0 148.0 156. 4

(SAE 50) Flash point, F- 420 410 350 550 530 460 Fire point, F. 485 460 385 630 610 530 Pour point, F. 25. -20 25 25 10 Color (ASIM)... 2% 2% 2 8 5 Conradson carbon residue, percent; 0.03 0. 07 0. 04 1.60 1.80 0. 40

Except for the viscosity index requirement however, the type and origin of the oil is not critical, and any of the conventionally-refined and solvent-extracted oils can be used.

The greases of the invention are prepared in accordance with conventional grease-making techniques. A small amount of the fatty acid mixture is charged into the kettle, melted if necessary, and then an amount of the mineral oil is mixed therewith, together with the stoichiometric amount of alkali 'oxide or hydroxide (fatty acid so'ap's can be used, if available). The mixture is agitated and heated at an elevated temperature within the range from 200 to 375 F. until saponification is complete. Thereafter, an additional portion of mineral oil is added, and additional amounts of the fatty acids and alkali are incorporated if required, until the grease reaches a penetration within the desired range.

Alternatively, the mixture can be formed by blending all of the soap with the oil and heating to from 200 to approximately 450 F. or the melting temperature, cooling to about 90 to 150 F. and then blending in any small additional amounts of the ingredients as required until the composition reaches the desired range of properties.

The grease components are heated to an elevated temperature within the range from about 300 to about 450 F. or heated to the melting temperature merely for a time sufiicient to insure thorough mixing, after which the grease is allowed to cool at once. The reaction temperature should not be so high as to cause chemical reaction of the grease components other than the formation of soap. Polymerization or dehydrogenation reactions involving the fatty acids or soaps thereof for example, are not desired and the heating at an elevated temperature is not continued for so long a time as to efiect such reactions.

inches high, equipped with double-action paddles, which were operated at a speed of 30 R. P. M. The paddles were operated by a link belt through a reducer driven by a A H. P. motor.

In preparing the grease, 6 lbs. of the particular fatty acid mixture was charged into the kettle, and melted if necessary, and then 4 lbs. of the mineral oil was mixed therewith, following which 2 lbs. of 45% sodium hydroxide was added, and the mixture was agitated and heated at about 280 F. until saponification was complete, as determined by usual operating procedures. After the reaction was complete, an additional 7 lbs. of mineral oil was added in increments and mixed into the base, and the base heated at 300 F. for one hour, and allowed to cool to 77 F. Additional amounts of the ingredients were added and blended, in. small amounts if necessary, until the grease had a penetration in the range of 265-295 at 77 F.

While the amount of the soap may be varied within the range disclosed, depending on whether a soft or hard grease is desired, the amount of soap in these tests was kept constant within the range of 18 to 22% to give a grease having a penetration within the range of 265- 295 at 77 F. in order to study the effect of the fatty acid gpon the consistency stability and the oxidation staility.

The acid mixtures used in the examples were commercially available, and were obtained from natural mixtures of fatty acids that were brought to the required iodine value by extraction, distillation, hydrogenation, dimerizing or addition of unsaturated or saturated acids, as the properties of the commercial material required.

The results in the following tables are typical of a large number of tests.

TABLE IV Example No. 1 2 3 4 5 6 7 Fatty Acids- Composition Stearic, 24%; Olelc, 63%; Oleic, 84.31%;

' Palmitie, 13%. Palmltic, 15.5%;

Llnoleic and Linolenic, 0.19%.

Iodine value 56. 4 56. 4 56. 4 56. 4 56.4 76. 2 76. 2 Wt. percent polyolefinic- 0 0 0 0 0. 19 0. 19 Wt. percent used in greas 16. 2 16.2 17.1 16.2 19.0 15. 8 17. 1 Grease preparation, temp. in 300 450 300 300 450 300 300 Grease Properties:

Penetration at 77 F. after working strokes 240 265 270 240 245 275 265 265 280 280 260 270 295 265 10,000. 305 295 295 295 300 310 295 Percent gain in penetration after 10,000 relative to 0 strokes 27 11 9 23 23 13 11 Oxidation, in p. s. 1. loss after 100 hours at 210 F.

under oxygen at 110 p. s. 1. initial pressure 1.0 1. 0 1.0 4.0 1. 5.0 5.0

TABLE V Example N o A B O D E F G H Fatty Acids:

Composition Stearic, 90%; Steal-1c, 48%; Stearic, Stearle, 2.5%; Oleic, 78%; Palrnitie,

Palmitie, Oleio, 7%; Oleic, 52%; 01210, 30.5%; Palmitic, 7.7%; 28.5%; Ste- 10%. Palmitic, Palmitic, Linoleic and Linoleie, 14.3%. aric,

%. 18%. Linolenic, 33.8%; 71.5%. Palmitic, 33.2%.

Iodine value 2. 3 6. 2 46. 4 89.4 89. 4 95. 8 95. 8 1. 1 Wt. percent polyo]efinic 0 0 0 33. 8 33.8 16. 9 16.9 0 Wt. percent used in grease. 17. 1 17. 1 14. 5 17. 1 20. 7 17. 1 19. 1 17. 1 Grease preparation, temp. in F 450 300 300 450 300 300 450 300 Grease Properties:

Penetration at 77 F. after working strokes- 0 220 190 220 260 310 280 270 310 280 310 340 290 340 290 260 330 0, 0 360+ 360+ 360+ 330 360 305 300 360+ Percent gain in penetration after 10,000

relative to 0 strokes 63+ 90+ 63+ 16 Oxidation, in p. s. i. loss after 100 hours at 210 F. under oxygen at 110 p. s. 1. initial pressure 3.8 3. 5 3.8 18.0 28.0 12 0 12.0 15 6 1 Used in the form of their glycerides.

The greases prepared in accordance with the invention, as set forth in Table IV, show a penetration gain after working 10,000 strokes of not over about 27%, and an oxygen pressure loss of not over 5, under the test conditions. These results are attained with fatty acids having iodine values in the range of 56.4-76.2, and having a polyolefinic acid content in the range of 0 to 0.19% by weight of the fatty acid.

The results in Table V show that greases prepared from fatty acids having a low iodine value, c. g., 2.3 to 46.4 have very poor consistency stability, as indicated by a gain in penetration after working 10,000 strokes of over 63% as shown in Examples A, B and C. The Table V data also show that greases made from fatty acids having too high a content of polyolcfinic acids have very poor oxidation stability, e. g., a 12 to 28 p. s. i. loss for 16.9 to 33.8% polyolefinic acid, under the test conditions, as shown by Examples D, E, F and G. Preferred greases are those showing a loss of less than 5 p. s. i. and greases which test a p. s. i. loss of more than 10 are regarded as unsatisfactory.

The greases prepared in accordance with the invention show distinct improvemcnis in consistency stability and oxidation stability over usual type greases, e. 5.3., over the usual type greases prepared from commercial grades of olcic acids, which acids are reported as having an iodine value of 85 to 110; and these acids contain substantial proportions of polyolcfinic acids. Comparable grease lubricants to those described in the Table IV examples may be prepared in accordance with the invention containing a mineral lubricating oil and 5 to by weight of a metal soap of a fatty acid having from 14 to 22 carbon atoms in the molecule, and having an iodine value in the range of to 77 and substantially free of polyolefinic acids, i. e., not over about 5 to 10% based on the weight of the acid. Greases made from acids having lower iodine values tend to be deficient in consistency stability," and greases made from fatty acids having too high a content of polyolefinic acids tend to have too low an oxidation stability.

Greases prepared in accordance with the above procedures, except using the corresponding glycerides instead of the free fatty acids, as shown in Example H do not have sufiicient oxidation stability to pass the above test. This indicates that the grease should be substantially free of glycerin or glycerin reaction products. A

grease could be prepared by converting a glyceride to the corresponding metal soap, recovering the soap free from glycerin reaction products, and then blending the soap with a mineral lubricating oil; however, for reasons of economy, quality of product, and facility of production, the above described method starting with the glycerin-free fatty acid is preferred. In general, grease lubricants often contain a small amount of free caustic, e. g., 0.1 to 0.2% by weight, or less.

The mineral oil used as the grease base should have a viscosity index of not over 87. The oil may have any lubricating viscosity, i. e., to 5000 SSU at F. The viscosity of the oil may be selected in order to give a grease having different penetrations, but this can also be offset by varying the amount of soap, as explained heretofore.

While the examples employ a sodium soap in compounding the grease in order to compare the variables which give novelty to the product, any other commercial grease-forming soap may be used, the principal soaps being formed from alkali and alkaline earth metals, such as lithium, calcium, and barium.

The expression consisting essentially of as used herein, is not intended to exclude components which do not alter the grease character of the composition or components which are conventionally added to greases, such as graphite, mica, and solids used in greases, ingredients to increase tackiness, oxidation inhibitors, extreme pressure and similar type additives.

The foregoing descriptions are for purposes of illustration only, and variations and modifications thereof may be made within the scope of the appended claims.

This application is a continuation-impart of application Serial No. 181,926, filed August 28, 1950, and now abandoned.

We claim:

1. A grease having a high consistency stability and high oxidation stability, consisting essentially of a mineral oil of lubricating viscosity having a viscosity index of not over 87 and having dispersed therein by heating to a temperature not in excess of approximately 450 F. about to 50% of a normal grease-forming metal soap of fatty acids having from 14 to 22 carbon atoms and an iodine value in the range of 55 to 77, the said normal fatty acid soaps being the sole fatty acid soaps in the grease, being substantially free of polyolefinic fatty acids, and being substantially free of glycerin and glycerin reaction products.

2. The grease of claim 1 wherein the metal is sodium.

3. The grease of claim 1 wherein the fatty acid components of the soap correspond to 16 to 18 carbon atom fatty acids and the amount of soap is to 30%.

4. The grease of claim 3 wherein the metal is sodium.

5. The grease of claim 1 wherein the fatty acid components of the soap correspond to 18 carbon atom fatty acids having an iodine value of about 76 and a polyolefinic acid content of not over about 0.2% of the weight of the acid.

6. The grease of claim 5 wherein the metal is sodium.

7. A method of preparing a grease having high con-- sistency stability and high oxidation stability, which method comprises dispersing at a temperature not in excess of approximately 450 F. in a mineral oil of lubricating viscosity having a viscosity index of not over 87 about 5 to of fatty acids having from 14 to 22 carbon atoms and an iodine value in the range of to 77, the said fatty acids being the only fatty acids in the grease mixture, being substantially free of polyolefinic fatty acids, and neutralizing the free fatty acids with a reactive metal compound yielding a normal grease-forming soap.

8. The process of claim 7 wherein the grease is heated to 300 F., after neutralization.

9. The process of claim 7 wherein the metal compound is sodium hydroxide.

10. The process of claim 9 wherein there is used 16 to 18 carbon atom fatty acids to form soap in an amount of 10 to 30%.

11. The process of claim 9 wherein there is used 18 carbon atom fatty acids having an iodine value of about 76 and a polyolefinic acid content not over about 0.2% of the weight of the acid.

12. The process of claim 7 wherein the grease is melted at a temperature of at least 450 F., after neutralization.

13. The process of claim 12 wherein the metal compound is sodium hydroxide.

14. The process of claim 13 wherein there is used 16 to 18 carbon atom fatty acids in an amount to form 10 to 30% soap.

15. The process of claim 13 wherein there is used 18 carbon atom fatty acids having an iodine value of about 76 and a polyolefinic acid content of not over about 0.2% of the weight of the acid.

References Cited in the file of this patent UNITED STATES PATENTS 2,265,791 Zimmer et al. Dec. 9, 1941 2,431,760 Licata Dec. 2, 1947 2,495,651 Butcosk Ian. 24, 1950 2,581,127 Morway et al. Jan. 1, 1952 2,588,280 OHalloran et al. Mar. 4, 1952 2,595,557 Worth et al. May 6, 1952 OTHER REFERENCES Lubricating Greases, Klemgard, pub. 1937 by Reinhold Pub. Corp. of New York, pages 55, 56, 58, 59, 62, 382 and 387. 

1. A GREASE HAVING A HIGH CONSISTENCY STABILITY AND HIGH OXIDATION STABILITY, CONSISTING ESSENTIALLY OF A MINERAL OIL OF LUBRICATING VISCOSITY HAVING A VISCOSITY INDEX OF NOT OVER 87 AN HAVING DISPERSED THEREIN BY HEATING TO A TEMPERATURE NOT IN EXCESS OF APPROXIMATELY 450*F. ABOUT 5 TO 50% OF A NORMAL GREASE-FORMING METAL SOAP OF FATTY ACIDS HAVING FROM 14 TO 22 CARBON ATOMS AND AN IODINE VALUE IN THE RANGE OF 55 TO 77, THE SAID NORMAL FATTY ACID SOAPS BEING THE SOLE FATTY ACID SOAPS IN THE GREASE, BEING SUBSTANTIALLY FREE OF POLYOLEFINIC FATTY ACIDS, AND BEING SUBSTANTIALLY FREE OF GLYCERIN AND GLYCERIN REACTION PRODUCTS. 